Polyolefin-based adhesives are useful for bonding polyolefins with polar materials such as nylon, ethylene vinyl alcohol copolymer (EVOH), and metals. Polyolefin-based adhesives commonly comprise maleic anhydride-grafted polyolefins. The grafting is usually performed by visbreaking, with or without free radical initiator, the polyolefin in the presence of maleic anhydride to cause formation of free radicals on the polymer chains that react with maleic anhydride. The grafted polyolefin is typically let-down with additional polyolefin resins to a desired concentration and to provide a polyolefin-based adhesive. See U.S. Pat. No. 4,487,885.
The grafted polyolefin can be let-down by a variety of polyolefin resins, including high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene, and ethylene-vinyl acetate copolymers. High performance adhesives also utilize a polyolefin elastomer as a let-down resin. In the known processes, the elastomer is premixed with other let-down resins and the mixture is then blended with the grafted polyolefin. Alternatively, the grafted polyolefin, elastomer and other let-down resins are simultaneously blended.
There is a need for an improved process for producing polyolefin-based adhesives that give better clarity and adhesion in multilayer polyolefin film application.